In many aircraft, the main propulsion engines not only provide propulsion for the aircraft, but may also be used to drive various other rotating components such as, for example, generators, compressors, and pumps, to thereby supply electrical and/or pneumatic power. However, when an aircraft is on the ground, its main engines may not be operating. Moreover, in some instances the main propulsion engines may not be capable of supplying the power needed for propulsion as well as the power to drive these other rotating components. Thus, many aircraft include an auxiliary power unit (APU) to supplement the main propulsion engines in providing electrical and/or pneumatic power. An APU may also be used to start the propulsion engines.
Many APU-equipped aircraft are operated in environments that have a high concentration of fine dust particles (e.g., <30 μm) suspended in the air. These fine dust particles, when ingested by the APU, can adversely impact the APU. For example, the fine dust particles can plug the holes in effusion cooled combustors, and can plug and corrode the high temperature turbine passages and hardware. To alleviate the adverse impact of dust particles, many aircraft include an inlet particle separator system (IPS).
Most IPSs are designed to separate out relatively large particles (e.g., 100 μm<1000 μm) but are less efficient at separating out fine particles. This is because these systems typically rely on particle inertia to move the particles into a separate collector and scavenge system. Fine particles, with relatively lower inertia, are much more inclined to follow the inlet airflow into the gas turbine engine, resulting in low separation efficiencies. Thus, many aircraft additionally include one or more systems to remove these fine particles. These additional systems include barrier filters (self-cleaning and non-self-cleaning), vortex panels, and multi-channel particle separator (MCPS) systems.
Although the three particle separator systems just mentioned do excel at removing fine particles from APU inlet airflow, they all exhibit certain drawbacks. In particular, each is designed to be relatively large in size in order to minimize pressure losses. This size requirement negates the ability to mount these systems inside the already existing APU inlet duct system.
Hence, there is a need for a particle separator system that can remove fine dust particles from APU inlet airflow, exhibit minimal pressure losses, and be incorporated into the APU air inlet system. The present invention addresses at least this need.